1. Field of the Invention
The present invention relates to a method for measuring an image ratio, for use in an image forming apparatus for forming an image by fixing a coloring agent to a recording sheet based on image data outputted from an image data supplying apparatus. The method is to be used for evaluating the characteristics of the image forming apparatus relating to the amount of consumption of the coloring agent or print agent, or for detecting the remaining amount of the print agent.
2. Related Background Art
In an image forming apparatus capable of image formation by depositing a coloring material or a print agent onto a printing medium, such as a laser beam printer or other electrophotographic printer which achieves printing by depositing toner particles onto the printing medium or an ink jet printer which achieves printing by discharging ink consisting of dispersion of a coloring agent such as a dye or a pigment onto the printing medium, there is provided means for measuring the amount of consumption of the coloring material or print agent by various methods. The information obtained by such measurement of consumption amount is not only important in evaluating the characteristics of the image forming apparatus but also is useful and important for the user in knowing in advance when the replenishment of the print agent becomes necessary.
For this reason, there have been proposed various methods for detecting the remaining amount of the print agent. For example, Japanese Patent Application Laid-Open No. 05-006092 proposes, for detecting the remaining amount of the developer, a so-called antenna method of detecting the electrostatic capacitance, which varies according to the remaining amount of the developer. Also, Japanese Patent Application Laid-Open No. 05-027593 proposes an optical sensor system in which an optical sensor is positioned on a replenishing path and an optical path is opened when the toner is entirely consumed, thereby indicating that the remaining amount of the toner has become less than a predetermined amount, and Japanese Patent Application Laid-Open No. 05-303281 proposes a system utilizing a piezoelectric element for detecting the remaining amount of the toner by the weight thereof.
However, these methods have not proved able, in case of a printing job of a large amount, to judge whether the toner or the ink is present in an amount sufficient for completing a current job, so that it sometime occurs that the exhaustion of the developer or the ink is detected in the course of the printing job, as a result of which the job is inevitably interrupted.
In this connection, as one of the means for measuring the consumption amount of the coloring material or print agent in an image forming apparatus, there is known a method of defining the image ratio as the area in which image formation is executed with respect to that of the print medium and acquiring the amount of the coloring material or print agent consumed in image formation on the print media of a predetermined number, based on such image ratio. More specifically, in a case of an image forming apparatus executing image formation based on digital image data, the image ratio is defined as the ratio (the so-called print ratio) of the number of pixels in which the coloring material or print agent is deposited to the number of total pixels of the image of the maximum size that can be formed by the image forming apparatus on the printing medium of a specified size.
However, that method for detecting the consumption amount of the coloring material or print agent has been associated with the following drawbacks.
The above-mentioned definition becomes valid in a case in which the image formation is executed by the presence or absence of deposition of the coloring material or print agent in each pixel, that is in a case of image formation based on binary image data. Therefore, the detection of the consumption amount of the coloring material or print agent based on such image ratio becomes relatively accurate, but the definition of the image ratio itself is problematic in a case of multi-value image data having tonal gradation, such as a photographic image. Particularly, in the case of full-color image formation, the image ratio cannot be appropriately defined for various reasons, such as (1) that the image data supplied to the image forming apparatus have various signal formats, such as the standardized RGB (Red, Green and Blue) data (sRGB data) or CMYK (Cyan, Magenta, Yellow and Black) data, and (2) that the relationship between the image signal and the consumption amount of the coloring material or print agent in the intermediate density range may be complex.